Scotchbrite wheels for polishing bronze

[Troy Scott]

Folks,

Yes I know all about patina and the way the metal protects itself. That's exactly what I'll be letting the bronze do...., later. Right now the opening ports are all removed because the boat is being repainted. I'll be rebedding the ports after the paint. I need to clean and return the ports to their original polished state before reinstalling them. I have tried the traditional cotton and sisal buffing wheels and various grades of polishing compounds and rouge, all with limited success. Apparently this isn't my forte. I've recently learned about the Scotchbrite polishing wheels for polishing. Have any of you used these? Did you have good luck? Any advice about which grits, etc.?

[Ron Churgin]

Hi Troy,

I am a Scotch Brite distributor so I can possibly help you. There is a somewhat bewildering array of product. Are you going to use a solid wheel on a bench grinder or a small wheel on a hand tool?

SB comes in flap wheels as well. The general rule of thumb is that the harder the wheel the more aggressive it is. Cut&Polish wheels tend to be most aggressive and will remove more metal. The EXL specs are less aggressive and will have more of a polishing or burnishing effect. A flap wheel works well for removing surface imperfections and handling marks. They even have combination wheels where they interleave Scotch Brite with coated abrasive sheets that give aggressive cut and a fine finish.

There is definitely an art to finishing and cleaning metal, it takes some practice to develop the touch. Some styles of wheels are more conformable to round shapes than others. You might find wheels with a marking like 2S Med. The lower the number the softer the wheel, the less material it will remove. S is for silicon carbide material. A is for aluminum oxide. S is good for bronze and generally is a sharper abrasive and will give finer finishes. If you have any questions about specific products let me know (you will be limited to what is generally available in retail stores...as ordering from the factory has some large minimum quantities). Also, I am not sure if you are just removing oxidation and discoloration or if you need to remove more material.

If you want to ask specific questions on the products you have available I would be glad to answer any.

Ron

[Ron M.]

Troy,
I've used Scotchbrite Roloc discs for years and they do a pretty good job cleaning up metal, use the ones for polishing to clean your bronze.
I had all my port lights and hatches out before I painted 4 or 5 years ago and used glass beads in a sand blaster to clean everything - #6 as I recall. Made quick work out of that project. I used a refridgerater carton for a sand booth with cheap polycarbonate sheets for windows, worked out great .......and when done threw it all away. The bronze ports looked so good I sprayed 4 or 5 coats of matt polyurethane on the interior surfaces.......and they still look good.
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[Troy Scott]

Ron Churgin,

Thanks for your response!

I will probably need to use both a bench polisher and a hand tool. The parts have some odd little areas that can probably be addressed better with a small hand-held tool.

I hope I'm understanding correctly that these wheels don't require the addition of polishing compounds to accomplish the work...? As I understand it the "grit" is actually in the wheel, right?

For most of my bronze, I don't need to remove metal at all. The metal was originally polished. I just want to return it to that state. I did buy one used opening port which is exactly like my original ones except that it was never polished. For that one I need to remove the sandy surface. So I need mostly polishing wheels and enough cutting wheels to bring one portlight (inside and outside) to a finely polished condition to match the others.

Do you think a trip to LOWES is in order, or would these products be more likely found in another venue? What about MSC?

I would appreciate some suggestions for specific products to look for. Thanks for your help!!

Ron Musk,

Do you have a part number for the particular Scotchbrite Roloc polishing disc that worked well for you? Do you think I could skip the bead-blasting step? Or is that pretty much mandatory? Did you use any polishing compound with the Roloc discs?

I do have a friend who owns a small sandblaster. What are "glass beads"? Could I use another media?

WRT the "four or five coats of polyurethane on the interior surfaces", did you use one-part polyurethane varnish or two-part polyurethane clearcoat? Are you familiar with bronze/brass lacquers like, for example "Staybrite"?

[Ron M.]

Troy,
Glass beads are not that abrasive, rather they kind of 'peen' the surface and are effective in cleaning surfaces where you don't want to remove the underlying material but get it absolutely clean. I think they are glass but could be polymeric........I'm not an expert on the subject.....can be reused many times.
I had a few cans of Helmsmen Spray Polyurethane left over from a previous job.......so I used that with good results.
I'm not sure of the Roloc's.......but I think green......not too aggressive.
Although it doesn't initially appear like much of a project it can consume a lot of time........that's why I blasted it. I did all ports, hatches, traveler arch and brackets. it was a good winter project.
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[Ron Churgin]

Hi,

You are correct, the abrasive is impregnated in the nonwoven nylon of the wheel. Norton also makes a similar product, trade name Bear Tex.

3M has a product called CPD5-R which can be ganged together on an arbor for light cleaning and givies a satin finish. For a fine or bright polish the cotton buff wheels with a rouge are your best bet. The cotton wheels take some trial and error to get the results you want.

As much as I hate to recommend my competition, MSC is a better bet than Lowes, they will have a greater selection. Good luck.

[Troy Scott]

Ron Musk,

Were your ports originally polished smooth? Or do they have the "sandy" finish from the casting? Is they are sandy, I can see where bead blasting makes the most sense. However, since mine were polished, I wonder if I would be "going backwards" if I blast them. Will blasting cause "dimples" in the original polished surface along with removing the verdigris?

Ron Churgin,

The problem I've been having with the polishing wheel/rouge route is that it's very hard/slow to get through the corrosion. Once I do it polishes nicely. It's also MESSY. The bits of cotton and rouge fly around the room and get gunk everywhere. That's not such a big deal, but I just want to get through with the cleaning/polishing as expeditiously as possible without doing any damage to the bronze. I will look for the CPD5-R and the Bear Tex. Thanks!

[Ron M.]

Mine are smooth on the exterior and somewhat rougher inside. I don't think beads will 'dimple' unless you focus blast on one spot too long. As with anything try a sample first. you can adjust air pressure if need be. All I needed was to clean them up and get all traces of silicon caulk removed, so the original surface remained unaffected by the process.
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[Ron Churgin]

As your experience has shown you, the cotton wheels and rouge are only good for polishing, making a bright shiny finish. You need something rougher for cleaning and removing discoloration. Its a progression. Like using progressively finer grits of sandpaper when finishing wood.

Sand blasting (which uses the glass beads, not sand) is a great way to clean up any parts that will fit in the compartment...much less labor intensive.

[Troy Scott]

Ron Churgin,

I bought some CPD5-R Roloc discs. I used one this evening on one of the bronze ports. I believe they are too aggressive. it quickly removes the corrosion, but it leaves the bronze visibly scratched. Do you have a suggestion?

[Ron Churgin]

Troy,

Possibly try flap wheels which come on a 1/4" shank CFFB-S S-FIN. Flap wheels tend to be less aggressive. All the SB wheels will leave some graining. For a polished bright finish you might need a buff and compound. 3M mentions in their catalog that EXL Unitized Deburring wheels can polish a wide range of metals and plastics and are cleaner than buffs and compounds. Go for the finest grit you can get.

Ron

[Jumping Flea]

I have removed my portlights to replace the teak interior panels and was planning to clean off the old silicone and other dirt/gunk. I did notice that the old silicone had green patina powder under it, making the silicone pop right off.

I hadn't thought about getting the patina off - but now that you mention it it does make sense.

So silicone will stick better to raw bronze?

jf

[Jumping Flea]

What is that hard, gray/black cement that Cape Dory used to bed the ports?

What should I use to fill holes where it's fallen out?

For rebedding portlights, is silicone the best adhesive?

Thanks for you advice,
jf

[Troy Scott]

JFlea,

As with you, the ruined teak plywood and some leaks are my reasons for removing and rebedding the portlights.

I think the acetic acid in the silicone (or whatever solvent in whatever silicone-like substance it is) reacted with the bronze over a 20 year period and caused the silicone and the gelcoat under it to turn green. It just doesn't make sense (to me) to reinstall corroded portlights. The sealant (I'll use polysulfide or polyurethane) has a better chance of sealing to a clean surface. Plus I intend to protect the bronze on the side toward the cabin.

I believe CD used gypsum powder in polyester resin (essentially homemade Bondo) to fit the portlights. This filled the void between the liner and the outer skin, so there would be a solid thickness to bolt through. I mixed an epoxy/mill fiber putty to fill in where it broke. I just waxed one of the portlight frames and used it as a mold.

I hope this helps.

[Ron M.]

Take it easy with polyurethane sealants... they are tenacious and VERY difficult to remove with out pulling chunks of boat off. Something like Boatlife or 3m 4200 will do the job.
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